The present invention relates to a power-assisted steering device for a vehicle, comprising control means operable to act on steering means, said control means comprising a transmission element in two parts, which parts are capable of limited relative angular displacement under the action of said control means, and power-assistance means which, in response to such angular displacment, act on the steering means in the same direction as the control means. These power-assistance means can comprise, in particular, a hydraulic unit, an actuator acting on the steering means and a distributor located between the unit and the actuator and having, for example, two rotors respectively rotating integrally with said two parts of the transmission element.
The relative angular play between the two parts of the transmission element is limited, by suitable stop means, to predetermined value, for example approximately 6.degree., which corresponds to 3.degree. on either side of a mean position of rest which is restored elastically, for example, by a torsion bar located between said parts. During normal operation, the stop means are not involved and as soon as the relative angular displacement between the parts begins under the action of the control means, the power-assistance means operate and actuate the steering means. If the power-assistance means should fail, the stop means become involved and enable the two parts of the transmission element to move together at the same angle in the desired direction, thus enabling the control means to take over manually to ensure stanby steering under direct control.
In the arrangements proposed hitherto, the stop means generally consist of a member which surrounds the two parts of the transmission element. This member which can, moreover, consist of one of the two rotors of the distributor is engaged with a certain play on the outer splines of one of the parts of the transmission element and without play or with a different play on outer splines of the other transmission element.
It has also been proposed that the stop means should consist of one end of one of the parts of the transmission element which is splined on the inside and which is engaged with play on outer splines of the other part of the transmission element.
In other words, the stop means act peripherally on the outside of at least one of the two parts of the transmission element. These know arrangements certainly have the advantage of high efficiency because of the considerable diameter along which the stop means act, but, on the other hand, they have the disadvantage of increasing the bulk of the assembly, notably in a radial direction. Furthermore, bearing in mind the little space which is available, they do not make it possible to choose freely the coupling means to make the rotors rotate integrally respectively with the two parts of the transmission element.
The object of the present invention is a power-assisted steering device for a vehicle of the type described above, in which these disadvantages are at least minimised and the bulk of which device is reduced, yet the device having at the same time, an excellent efficiency, the device also containing an advantageous embodiment of the means for coupling the rotors to the two parts of the transmission element.